1. Field of the Invention
The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that optically reads an image by reading reflected light from a document.
2. Description of Related Art
In an image reading apparatus, which is called a scanner, either a reading system comprising a linear light source or an object of image reading such as a document is moved in a direction perpendicular to the linear direction of the light source, so that an image is read two-dimensionally. As the light source, conventionally, a fluorescent lamp is used, but in these years, it is tried to use an LED.
Unlike a fluorescent lamp, an LED is a point light source. Therefore, in order to obtain linear light distribution, which is required for scanning, the light emitted from an LED must be changed to have linear light distribution by use of a light guide member, or a plurality of LEDs must be arranged linearly on a substrate.
Also, an image reading apparatus is demanded to read an image in a cubic area without shading, and for this purpose, it is necessary to illuminate an object of image reading from both sides of scanning. In a conventional lighting system using a fluorescent lamp, it is avoided to use two fluorescent lamps, which is costly, to illuminate an object from both sides, and in order to cut the cost, only one fluorescent lamp and a reflection mirror that are located opposite each other are provided. However, an LED has strong directivity and unlike a fluorescent lamp, cannot be used keeping a large angle of aperture, and when an LED is used as the light source, it is difficult to illuminate an object from both sides of a scanning direction.
Japanese Patent Laid-Open Publication No. 2004-170858 suggests that LEDs be disposed at both sides of a scanning direction to illuminate an object of image reading from both sides. Japanese Patent Laid-Open Publication No. 2005-102112 suggests that a convergent member be provided between an LED and an object of image reading and that part of light traveling toward the object be reflected by reflection mirrors located opposite each other to illuminate the object from the other side.
In the former structure, LEDs are provided at both sides, and a large substrate and complicated wiring are necessary, which inevitably results in an increase in cost. In the latter structure, light is diverged at the convergent member, which causes a large amount of diffused light and lowers the efficiency of using light. Also, stray light occurs, which results in degradation of image reading performance.